This invention relates generally to fuel injection control signals and, more particularly, to a control system for handling an overlap of one fuel shot with another fuel shot in a multi-shot fuel injection event.
Electronically controlled fuel injectors are well known in the art including both hydraulically actuated electronically controlled fuel injectors as well as mechanically actuated electronically controlled fuel injectors. Electronically controlled fuel injectors typically inject fuel into a specific engine cylinder as a function of an injection signal received from an electronic controller. These signals include waveforms that are indicative of a desired injection rate as well as the desired timing and quantity of fuel to be injected into the cylinders.
Regulations pertaining to engine exhaust emissions are becoming increasingly restrictive throughout the world including, for example, restrictions on the emission of hydrocarbons, carbon monoxide, the release of particulates, and the release of oxides of nitrogen (NOx). Tailoring the number of injections and the injection rate of fuel to a combustion chamber, as well as the quantity and timing of such fuel injections, is one way in which to control emissions of an engine and meet such emission standards. As a result, split or multiple fuel injection techniques have been utilized to modify the bum characteristics of the combustion process in an attempt to reduce emission and noise levels. Split or multiple injection typically involves splitting the total fuel delivery to the cylinder during a particular injection event into two or more separate fuel injections, such as a pilot injection, a main injection, and an anchor injection, which may each be referred to generally as a fuel shot. As used throughout this disclosure, an injection event is defined as the injections that occur in a cylinder during one cycle of the engine. For example, one cycle of a four stroke engine for a particular cylinder, includes an intake, compression, expansion, and exhaust stroke. Therefore, the injection event in a four stroke engine includes the number of injections, or shots, that occur in a cylinder during the four strokes of the piston. The term shot as used in the art may also refer to the actual fuel injection or to the command current signal to a fuel injector or other fuel actuation device indicative of an injection or delivery of fuel to the engine. At different engine operating conditions, it may be necessary to use different injection strategies in order to achieve both desired engine operation and emissions control. However, at higher engine speeds the controllability of distinct fuel shots relative to each other in such multi-shot injection signals is more difficult because of issues associated with high engine speeds. For example, if higher engine speeds are not accounted for, the total time duration of the fuel injection signals decreases, whereby the time delay between the end of one fuel shot and the beginning of a subsequent fuel shot may decrease. At significantly high engine speeds, the time delay may decrease below a minimum acceptable level, and the fuel shots may occur to close to each other or may even overlap, which situations are disadvantageous to the performance, fuel efficiency, and emissions of the engine. Even with more advanced electronically controlled fuel injectors, during high speed engine operating conditions, it is sometimes difficult to accurately control the timing of fuel delivery associated with each fuel shot despite the use of electrical current control signals.
Accordingly, in a system wherein multiple fuel injections and different injection waveforms are achievable, it is desirable to control the delivery of individual fuel shots in each fuel injection event so as to minimize overall emissions and fuel consumption. Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, there is disclosed an electronically controlled fuel injection system capable of delivering fuel injection signals, including a plurality of fuel injection shots, to the cylinders of an internal combustion engine during a single fuel injection event. The system includes at least one fuel injection device associated with each cylinder and operable to deliver the fuel shots, and a controller operable to determine the total desired fuel quantity, timing, number of fuel injections in an injection event, and actual fuel quantities associated with each individual fuel shot.
In one embodiment of the present invention, the controller is operable to provide fuel injection events comprising three distinct fuel shots, namely a pilot shot, a main shot, and an anchor shot. Each fuel injection event corresponds to a particular cylinder in an engine. The controller is further operable to determine whether the first shot, or the pilot shot, maintains at least a minimum desirable distance in time ahead of the second or main shot. If the pilot shot does maintain such minimum desirable distance, then the controller sends an appropriate fuel injection signal to the injection device associated with the respective cylinder. On the other hand, if the pilot shot does not maintain such minimum desirable spacing or distance, then that portion of the pilot shot which overlaps into either the minimum desired spacing between the pilot and main fuel shots or into the main fuel shot itself is removed, or the pilot shot duration is set to zero.